1. Field of the Invention
The embodiments of the invention relate to a transistor and a method for manufacturing the same, and more particularly, to an organic thin film transistor and a method for manufacturing the same.
2. Discussion of the Related Art
Generally, a thin film transistor is used as a switching element for a display device. The thin film transistor may be formed of various materials, such as silicon and organic materials. The organic thin film transistor is formed of an organic semiconductor material. The organic thin film transistor is formed on a flexible substrate instead of a glass substrate. Other than the organic thin film transistor using the organic semiconductor material and the flexible substrate, the organic thin film transistor is similar in structure to the silicon thin film transistor.
FIG. 1 is a cross-sectional view of illustrating the related art organic thin film transistor. As shown in FIG. 1, the related art organic thin film transistor includes a gate electrode 52a of a metal material formed on a lower substrate 51, a gate insulation layer 53 formed on the lower substrate 51, including the gate electrode 52a, source and drain electrodes 55a and 55b overlapping both edges of the gate electrode 52a and formed on the gate insulation layer 53, and an organic semiconductor layer 54 formed on the gate insulation layer 53 including the source and drain electrodes 55a and 55b. In this case, the source and drain electrodes 55a and 55b can be formed of a metal material, such as palladium (Pd) or argentums (Ag). However, if the source and drain electrodes of the organic thin film transistor are formed of a metal material, such as plumbum (Pb) or argentums (Ag), a metal patterning process for the source and drain electrodes is complicated and complex, and adhesive strength between the metal material and the organic semiconductor becomes weak.
The source and drain electrodes can be formed of a transparent conductive layer, such as indium tin oxide (ITO) and indium zinc oxide (IZO). The transparent conductive layer has the advantage of being easy to pattern. However, source and drain electrodes are formed of transparent conductive layers having a high contact resistance with the organic semiconductor layer. More specifically, if the source/drain electrodes are formed of transparent conductive layers, an energy barrier occurs at the interface between the transparent conductive layer and the organic semiconductor layer. Such an energy barrier prevents a charge injection so as to increase resistance between the transparent source/drain electrodes and the organic semiconductor layer. More specifically, the energy barrier interrupts the movement of majority carriers in an accumulation mode. Due to such a resistance increase between the organic semiconductor layer 54 and the source/drain electrodes 55a/55b, the mobility is lowered and current crowding occurs at low voltages, which degrades the operating characteristics of the thin film transistor.